Menstruation is not an issue in space travel. Gravity is not essential for menstruation to occur. Menstruation is a very complicated physiological process involving the internal factors of many different hormones, the woman's sexual organs, and the brain.

Very little blood is lost during menstruation. Thus, it is not considered a major "waste management" problem by space flight scientists. When menstruation occurs in a zero gravity environment it will have to be dealt with somewhat differently hygienically. But to do so is far less of a challenge for scientists than the far more important "waste management" problems posed by urination, defecation, infections, and a few other normal body processes and events that can be expected when humans travel in space.

Writing in the Obstetrical and Gynecological Survey in February 2000, Dr Richard Jennings and Dr Ellen Baker from the University of Texas Medical Branch in Galveston point out that: "There currently are no operational gynecological or reproductive constraints for women that would preclude their successful participation in the exploration of our nearby solar system."

Dr Baker is also an astronaut with the NASA-Johnson Space Centre in Houston.

Women have been an important part of space crews since almost the beginning of space travel in 1961. The first woman in space was Valentina Tereshkova who flew on the Soviet Union's Vostok 6 flight in 1963. In the US space program, the first woman in space was Dr Sally Ride in 1983.

There are gender differences in the ability to withstand extremes such as reduction in oxygen supply (hypoxia), heat, cold, decompression, acceleration, isolation, and "impact". However, as Drs Jennings and Baker observe, "these differences are generally minor, often depend on acclimatisation and individual variation, and favour women as often as men."

Interesting facts

The vast majority of women astronauts have not had children. Most delay their first pregnancy until their space career is over. Of these women, the average age of giving birth for the first time is 40.

It is certainly possible for humans to conceive in space. Such experiments were rumored to have taken place in some Soviet space flights, but were officially denied at the time.

NASA will not allow women astronauts to participate in neutral buoyancy training while pregnant. This involves dives underwater lasting up to eight hours. The pressure changes are thought to be potentially harmful to the developing baby.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au